1. Field of the Invention
The present invention relates to an automotive heating apparatus.
2. Description of the Related Art
A conventional general-purpose type automotive heating apparatus is constructed as follows: It supplies high temperature circulating water, which has been used for cooling an engine, to a radiator, thereby cooling the circulating water. At the same time, it also supplies a part of the high temperature circulating water to a heater, and thereby it carries out the heat exchange from the high temperature circulating water to air at the heater. Consequently, it supplies hot air to a passenger room. The circulating water going through the heater is again used for cooling the engine together with the return circulating water.
However, this conventional general-purpose type automotive heating apparatus cannot supply the hot air to the passenger room until the circulating water for cooling the engine becomes considerably hot in temperature. Therefore, especially under a relatively low temperature environment in cold areas or the like, it takes a long time to achieve the heating in the passenger room after the engine is started.
Hence, as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 246,823/1990, an automotive heating apparatus has been developed in order to achieve the heating in the passenger room relatively quickly after starting the engine. The automotive heating apparatus comprises a viscous fluid coupling which is connected to an engine cooling circuit.
the viscous fluid coupling of the recently developed automotive heating apparatus includes a housing, an input shaft rotatably disposed in the housing and receiving an engine driving force by way of an electromagnetic clutch, a rotor disposed in the housing, fixed to the input shaft and having a labyrinth groove including a plurality of and a large area of walls, a cover fixed to the housing and having a labyrinth groove engaging with the labyrinth groove of the rotor and disposed away therefrom with predetermined spaces provided therebetween, and a viscous fluid such as a silicone oil or the like sealed between the rotor and the cover.
In the viscous fluid coupling, the circulating water sealed between the cover and the housing is circulated with an engine cooling apparatus. When the input shaft is rotated in order to rotate the rotor, the viscous fluid sealed between the rotor and the cover is caused to generate heat by the stirring and the shearing resulting from the relative rotation between the rotor and the cover. The heat thus generated is conveyed to the circulating water sealed between the cover and the housing, and thereby heating the circulating water. Finally, the circulating water thus heated is used for the heating in the passenger room through a heater.
However, the recently developed automotive heating apparatus set forth in the aforementioned publication employs the viscous fluid coupling whose rotor and cover have the labyrinth grooves including a plurality of and a large area of walls, respectively, and accordingly it is liable to enlarge. Namely, the automotive heating apparatus requires a large installation space in an engine room with a limited space provided, and accordingly it suffers from the on-boardability. Moreover, in the manufacture of the automotive heating apparatus, the rotor and the cover require complicated processing, and accordingly the manufacturing cost is increased inevitably.
In addition, as illustrated in FIG. 10, the recently developed automotive heating apparatus set forth in the aforementioned publication cannot avoid or interrupt the proportional relationship between the driving torque "T" of the input shaft and the number of engine revolutions "N" without turning on and off an electromagnetic clutch in an ordinary service area, e.g., the number of engine revolutions "N" between "n.sub.1 " and "n.sub.2." Namely, the automotive heating apparatus requires a large power "L" and outputs a large heat generation during high speed automotive driving, and accordingly it increases the engine load and provides an excessive heating capacity. In order to avoid this drawback, it is necessary to frequently turn on and off the electromagnetic clutch during the high speed automotive driving. However, the electromagnetic clutch is deteriorated by the frequent turning on and off operation in a short period of time, and eventually no comfortable automotive driving feeling cannot be obtained.